We are studying the cone inputs to spatial detectors in human vision using Stile's two color method to isolate the chromatic pi mechanisms. The pi mechanisms are isolated with a test target of one color on a field of a different color. The shape of the spectral sensitivity of most pi mechanisms resembles the shape of the spectral absorption of rhodopsin. Thus mechanisms may reflect distal visual processes. Superimposed patterns of different colors, however, show that different, presumably isolated pi mechanisms may strongly interact, often in an antagonistic manner. We are studing such interactions with monochromatic gratings generated directly on the retina as interference patterns of laser light. We are examining the hypothesis that at low spatial frequencies, the red and green pi-mechanisms may show strong color-opponent interactions especially when the adapting field is bright. The same mechanisms, however, may act additively or independently at high spatial frequencies. The blue pi mechanisms may act relatively independently at low spatial frequencies during steady-state adaptation; however at spatial frequencies of 7-16 c/deg the adaptive state of the blue mechanisms may be strongly controlled by the red and green pi mechanisms. At higher spatial frequencies the blue pi mechanisms are insensitive.